1. Field of the Invention. This invention pertains to balancing machines, and more particularly to apparatus that qualitatively indicates imbalance in rotatable objects.
2. Description of the Prior Art. Various equipment has been developed to determine and eliminate mechanical imbalance in rotatable objects. Such equipment assures that the mass of the object is symmetrically distributed about its axis of rotation. Failure to correct imbalance results in well known detrimental effects to both the rotating object and to the structure to which the object is mounted.
Rotatable objects are invariably balanced by adding or subtracting mass at appropriate locations on the object. For example, it is known to add small weights to an object diametrically opposite the location of an eccentric center of mass. Alternately, material may be removed in radial alignment with and on the same side of the axis of rotation as an eccentric center of mass. Numerous balancing machines are in present use for performing the foregoing balancing procedures.
The capabilities of prior balancing equipment vary considerably. To suit the requirement of a particular application, some equipment is very sophisticated, having the ability to both measure and correct object imbalance on an automatic basis. Such equipment is expensive to manufacture, and skilled personnel are required to operate it. Other applications require more modest demands of the balancing machinery. For example, some balancing machines are capable of only measuring imbalance, while other machines are capable of only correcting imbalance.
A particularly important application of balancing machines concerns rotatable objects that are long, narrow, and thin. A typical example is a lawn mower blade. Lawn mower blades rotate at very high speeds. Further, in many lawn mowers, the blade acts as the flywheel for the internal combustion engine that powers the lawn mower. It is therefore vital that the blade be accurately balanced.
In addition to the actual balancing, another very important requirement must be met in the case of lawn mower blades. The blades are subject to very hard use, and even abuse, during the normal course of their operation. Consequently, the blades must be periodically removed from the lawn mowers and serviced. That is in contrast to many rotatable objects whose balance characteristics do not change with use and so need be balanced only when they are initially placed into service. When the frequent servicing factor is considered in light of the relatively low initial cost of a lawn mower blade, the requirement arises that lawn mower blades must be balanceable at a very low cost. That is, it is an economic necessity that a blade be rebalanced for only a few dollars. Accordingly, low cost equipment is used to service lawn mower blades, and different machines are usually used to determine the amount and location of imbalance and to correct the imbalance.
An example of a prior machine for determining the amount and location of imbalance in a lawn mower blade and the like may be seen in U.S. Pat. No. 2,987,924. In the balancer of that patent, a cylindrical tube having a cone on one end is mounted on bearings for rotation about a horizontal axis. A strong magnet is accurately slidable along the cylindrical tube. A mounting hole in the lawn mower blade is centered on the cone, and the magnet is slid along the tube until it contacts and holds the blade firmly in place with the plane of the blade being perpendicular to the horizontal axis. If the weights of the two blade ends are unequal, the tube, cone, and blade will rotate under the influence of gravity such that the blade heavier end lies under the lighter end. Then the blade is pulled from the balancer and taken to another machine for removal of material.
A balancing application somewhat related to lawn mower blades concerns industrial and commercial saw blades. Such blades are very thin and have relatively large diameters. Their mounting holes are often tapered. U.S. Pat. No. 3,659,463 shows an example of a machine for qualitatively determining the imbalance of saw blades.
The balancing machines of the 2,987,924 and 3,659,463 patents have been in commercial use for many years and have contributed to the balancing of countless lawn mower blades, saw blades, and the like. Nevertheless, they are subject to improvement.